This PDF file contains the editorial “Editorial: A Specific Question of Ethics” for OE Vol. 34 Issue 12

This PDF file contains the editorial “Guest Editorial: Optics in Polymer Science and Technology” for OE Vol. 34 Issue 12

The electric polarizabilities of cumulenes are calculated with the aid of the free-electron theory for r electrons moving along the chain of the carbon atoms. The calculations done for different frequencies of the incident light are compared with the results of the Pariser-Parr-Pople theory. Similar calculations of the positions of the lowest absorption maxima for cumulenes include the electron-electron interaction and are compared with the experimental data.

The material is presented for those who intend to use polarization modulation and phase-sensitive detection methods in their work. The know-how is presented on optical and electric components used in polarization-modulation instruments. Three essentials in polarization-modulation spectroscopy-the Mueller matrix approach, the photoelastic modulator (PEM), and the phase-sensitive detection method-are intensively discussed. How versatile and powerful the Mueller matrix approach is in the analysis, evaluation, and understanding of problems associated with polarization-modulation measurements is shown. Use of the Mueller matrix approach in the interpretation and design of experiments in polarization modulation spectroscopy is recommended

Quantitative data on the crystallization kinetics of polymorphic polymers can be derived from the investigation of gross spherulitic morphology formed in isothermal conditions. Depending on distance between centers, and the time lag between their formation and relative growth rates, various types of boundary lines can be generated by the impinging of two spherical bodies whose radii increase linearly with time. In polymorphic polymers, different types of spherulites often develop simultaneously at different rates from sporadic or predetermined nuclei. In some cases, the so-called growth transformation, in which a nucleus of the fast growing specie is formed at the tip of an advancing lamella of the slower crystal form, provides an alternative mode of nucleation. It is shown that if only one event of growth transformation takes place at the front of a slow growing body, the fast growing spherulite swallows the parent one and the resultant shape of interspherulitic boundary is described by two symmetrical logarithmic spirals whose parameters can be extracted from micrographs taken at the end of crystallization. These concepts are applied to determine the radial growth rate of γ form spherulites of polypivalolactone in a wide range of temperatures through analysis of the α/γ interspherulitic profiles formed in isothermal conditions and direct measurement of the growth rate of the α counterparts at the same temperature.

A system for experimental investigations of phase transitions under the electric field by means of polarizing microscope is described. The microscope is equipped with a video camera and a video digitizer, enabling the acquisition of patterns directly into the computer memory. The application of the system to the measurements of crystallization kinetics of polymers with and without an electric field is shown. The physical background of crystallization kinetics in polymer systems is also given.

A new method of determining the characteristic parameters in nonhomogeneous polymers is described. The method makes it possible to measure the characteristic parameters for a large region of the sample in a fast and simple way. The measurements are made by means of a modified polarizing microscope, serving as a micropolariscope. Characteristic parameters are determined for epoxy resin with different spherical inclusions: glass, poly(vinyl acetate), and an air bubble. It is concluded that retardation images are related to the type of inclusion. The analysis of characteristic direction images is more complicated because they depend on the position of the inclusion within sample thickness.

We report the results of a temperature study of the optical Kerr effect in 1,4-butanediol dimethacrylate revealing a phase-transition-like change in the temperature range from 295 to 302 K. Using the Brillouin light-scattering method, we studied the temperature behavior of the sound velocity and the elasto-optic constant of 1,4-butanediol dimethacrylate. The preceding temperature dependences display also characteristic discontinuity at about 298 K. To verify these results, a study of the Raman light scattering in 1,4-butanediol dimethacrylate was performed in the same temperature range. It was found that the temperature dependence of the relative intensities of the bands corresponding to the C = C, C = 0, and = C-H bonds reveals a discontinuity at about 294 to 297 K, which coincides with the observed temperature discontinuity of the optical Kerr effect and the Brillouin light scattering. The obtained results are discussed in terms of changes in molecular interactions and the arrangement in the liquid compound investigated.

The method of determining the orientational order in uniaxial phases of anisotropic matrices based on the polarized absorption and fluorescence spectra is described. The application of this method for three liquid crystalline side chain polymers in uniaxial smectic and nematic phases is presented. Based on the experimental data, the order parameters ⟨P2⟩ and ⟨P4⟩ and the molecular distribution function f(β) versus temperature are obtained.

Nonlinear M-line spectroscopy is based on the analysis of the nonlinear change in the shape of the dark line associated with the excitation of guided waves. This is an easy technique for the determination of Kerr properties of thin films, which can constitute optical waveguides. Full spatiotemporal nonlinear modeling tools have been developed recently for nonlinear waveguide couplers, which are used for the determination of the complex nonlinear coefficient of organic polymers.

A brief review of photoelastic materials comprising primarily high-sensitivity polymers and their mechanical and optical properties is presented. This review is followed by a discussion of their advantages, disadvantages, and the ranges of their applicability. The main selecting criteria of proper materials for photoelastic studies are listed and the relations between the chemical structure of polymers and their photoelastic and mechanical properties are discussed. The calibration methods are briefly described.

The interference effects in the centers of "disklike" whole cylinders of different photoelastic materials loaded by uniaxial forces acting along diameters are studied. The intensity of the light passing through the cylinder is analyzed and a few numerical models of the phenomenon are constructed and compared with the experimental results. The dispersive character of the "photoelastic constant" is shown and its consequence for the effect are emphasized. A computer-aided spectrometer was specially constructed for the research and is the heart of a semiautomatic measurement stand. The utilization of the effect to construct an optical force sensor is shown.

A brief description of the basic optical and electro-optical effects observed in polymer-dispersed liquid crystals (PDLCs) is presented. Theoretical models of light scattering from such structures and measurement techniques of PDLC optical properties are included, based on which of the material properties of polymer and liquid crystal required for application are discussed. Special attention is paid to the methods for optimizing PDLC optical and electro-optical properties. Finally, the known and possible applications of PDLC optical properties are discussed.

Confocal optical microscopy augmented by the phase-sensitive detection technique has been used to determine the erbium ion distribution in the core of single-mode optical fibers. The fluorescence at 565 nm generated by erbium ions under 488 nm excitation has been used to map the distribution of these ions in several doped fibers and the total ion concentration was estimated. The minimum concentration of erbium ions that can be measured using this technique is estimated to be of the order of a part per million.

The design of kinoform fan-out elements with high efficiency and reduced sensitivity to vertical profile scaling errors is presented. We start from a high-efficiency continuous-phase fan-out solution and optimize the position of the 0-2π transitions in the phase function, in order to achieve a high fabrication-error tolerance. The sensitivity of Fourier-transform and focusing fan-out elements to vertical etch-depth errors is analyzed. The limitations for the fabrication of such structures by laserbeam writing are discussed. In particular, the influence of the finite writing-spot diameter on the fan-out performance is investigated. Design rules for fan-out elements, which consider fabrication constraints, are derived. Experimental results are presented for cylindrical focusing fanout elements with small uniformity error (2%) and weak profile scaling dependence.

Tapered fiber tips with different geometries are fabricated for developing a fiber optic biosensor. Fluorescence experiments are performed to compare the coupling efficiency of light for different fiber tip configurations. When light is generated in a "thick" layer (> 1 μm) around a fiber core, the continuously tapered tip with the steepest taper collects light more efficiently than the longer combination tapered tip. To demonstrate the applicability of our results, we have successfully detected weak chemiluminescent signal collected by a bundle of fibers with the short continuously tapered tips using a cooled CCD array detector. The chemiluminescence reaction was catalyzed by alkaline phosphatase immobilized on the fiber tips by a sol-gel technique.

Although several models exist for calculating the loss in a fiber optic butt-joint resulting from angular misalignment between the fiber ends, these models generally assume an even energy distribution both across the face of the emitting fiber and throughout the emission angle. We present a numerical method that allows for arbitrary and physically realizable energy distributions. This approach also takes into account the physical size of the cladding on joint geometry, a previously neglected factor that becomes important for large tilt angles. Our results show loss curves that are appreciably different from those predicted by simpler models.

We propose a method for signature verification based on natural-handwriting motion segmentation. Dynamic segmentation of the handwriting motion in accordance with motor commands is used to better correlate authentic signatures and to better reject forged ones. Utilization of personalized adaptive thresholds in signature segmentation and verification stages proves to produce good dissimilarity measures. Experiments show that 90% correct classification can be achieved.

The problem of correlation wavefront sensing using an extended arbitrarily structured target as a light source is studied. The principle of extended target correlation wavefront sensing employing an intensity-transmittance type of mask is analyzed. The problems of simulation and selection of a target in laboratory experiments are discussed. The methods of generating the mask images from the target structure and of preparing the experimental masks from the mask images are presented. Typical results of the mask images generated by processing the target image are given. The preliminary experiment on the extended target wavefront sensing using the intensity-transmittance type mask are made. The effects of two different intensity-type masks on wavefront sensing are compared. Experimental results that are in agreement with the theory are obtained.

An image sequence containing a missile in flight often contains a strong plume signature expelled by the missile along with a weak signal corresponding to the missile hardbody. Enhancement of the missile signal is necessary to accurately track the trajectory throughout the image sequence. A parametric motion estimation algorithm is proposed for the passive stabilization of the data set. By stabilizing the image sequence with respect to the missile vacuum core, a registered sequence is produced with the missile located in the same position within each frame. Missile contrast can then be enhanced by applying a novel technique known as product correlation to the stabilized data. Product correlation is presented in the context of higher order statistics, and it offers a computationally efficient means of obtaining sample moments of high orders collectively. Simulations with missile sequences acquired in the IR and visible portions of the spectrum show that image stabilization followed by product correlation successfully enhances missile signal contrast, particularly in image sequences characterized by low SNRs.

An all solid state integrated optical cellular two-layer logic image processor, which can be used for binary image processing, has been designed and fabricated. The first layer is an optical parallel self-programming logic processor, constructed with prism combinations. The second layer is an optical, morphological dilation processor assembled with birefringent plates. The complete system uses the direct cascade of these two processors. It is shown that the integrated system is compact in structure, insensitive to environmental influences, and efficient in performance.

We present a technique for evaluation and selection of features based on an entropy measure with 1-D K-means clustering of individual features. The technique compares favorably with a combinational selection technique based on the Euclidean distance separability measure in terms of computational requirement. Experiments on the handwritten numeral recognition problem using the multilayer perception classifier show that the technique can reliably evaluate features and successfully select those ones important for performing the classification using a system of reduced complexity with little degradation of the performance. The technique can also be used to discard the noise-corrupted features in order to increase the reliability of a classification system.

Binary computer-generated holograms have been produced using different output displays, with different techniques, resolutions, and material substrates. Laser printers, commercial high-resolution laser writers, and lithographic techniques have been used. A combined technique based on the photoreduction over a lithographic plate of a mask generated by a high-resolution laser writer is proposed. We have studied the impulse response of such holograms and their performance with a view to their use as filters in correlation setups for pattern recognition. The results obtained show that lithographic techniques improve the quality of the holograms. The holograms obtained with the combined technique are comparable, for this application, to those etched directly onto the lithographic plate.

A phase-shifting digital speckle pattern interferometer (DSPI) has been calibrated using a Michelson interferometer. Calibration consists in measuring phase shifts generated by piezoelectric transducers (PZTs) and also to determine drift of the phase with time in the interferometer arms. The calibration fringes are displayed live on the TV monitor and then processed slice by slice after recombination following their recording sequence (PZT voltage or time). Dark fringes are detected to compute the wavelength with good accuracy (λ/170 theoretical) and the optical path difference is stored in a datasheet for every slice. This leads to the measurements of the drift and the calibration of the phase shifters with an accuracy about λ/20. Out-of-plane and in-plane optical fiber DSPIs have been successfully characterized using the same algorithm. The method presented also enables inexpensive data processing. Moreover the real-time measurement of the interferometer drift enables feedback loop active control during DSPI measurements.

Usually, rough surfaces cannot be measured by interferometric methods because the wavefronts are disturbed by speckle noise. This problem can be overcome by an increase of the test wavelength. One way to increase the effective wavelength is to use grazing incidence interferometry. We suggest an interferometer specifically adapted for the measurement of cylinders or tubes. Reference and object wavefront are generated using problem-specific computer-generated holograms as beamsplitters. The method can be extended to other geometries. We introduce the principle and show first experimental results.

Due to the increasing environmental limitations imposed on the chemical materials used in optical glass production, there is now an economic desire to minimize the number of glasses used in lens design. This paper presents the results of a study to create a glass listing that contains the minimum number of glasses needed for most lens designs. A double Gauss lens is used in the glass selection process. As part of this study, the relationship between the error function and the number of glasses chosen, as defined by a glass-count study, is found, as is the relationship between the error function and the location of a particular glass, as defined by glass-range study. Three lens libraries were studied using the global optimization method, and the most frequently chosen glasses were then compiled into the recommended glass listing according to the glass-count and glass-range studies. A recommended glass listing with nine glasses constructed from this study is presented.

We employ a Monte Carlo ray-tracing technique to model light-extraction characteristics of light-emitting diodes. By keeping track of the various processes that photons can encounter in a packaged LED, consisting of a semiconductor chip, a reflector dish, and an epoxy magnifying lens, our model can provide valuable information for LED design. The simulations can be performed very effectively on modern workstations. Preliminary results from a sample parametric study indicate that, with some refinement, our method could be used as a computer-aided design tool for optimizing light-extraction efficiencies and for designing LED spatial emission characteristics.

Nematic liquid crystals were put into the micropores of anodic alumina films. Molecules of a liquid crystal tend to orient along the axis of columnar pores, since the pore diameter is smaller than 0.2 μm. Accordingly, the refractive index of the liquid crystal varies with the polarization of the light that propagates in the alumina film; i.e., the ordinary and extraordinary indices (n_o and n_e) correspond to polarizations that are vertical and horizontal to the pores, respectively. The anisotropy in refractive index causes a prominent polarization function due to the index mismatch between a liquid crystal and alumina (n = 1.64). When a liquid crystal of n_o = 1.50 and n_e = 1.64 is used, the optical loss for vertical polarization is larger than that for horizontal polarization by more than 10 times at 0.85- to 1.30-μm wavelengths. If one coats lecithin on the pore walls, molecules of a liquid crystal orient nonuniformly in the pores. Then the refractive index becomes nonuniform, and consequently, significant light scattering occurs inside the pores. The optical loss tends to decrease at shorter wavelengths and in alumina films with smaller pores.

The diffraction efficiencies of binary-optics lenses with low f/#'s deviate from predictions of scalar diffraction theory. To increase the diffraction efficiencies for low f/#'s, vector diffraction theory is necessary. In this paper, we describe the design and fabrication of a 30 x 50 array of f/1 binary-optics microlenses using direct-write electron-beam lithography and reactive-ion etching. The diameter of each lens is 160 μm, and the focal length is 165 μm. The center-to-center spacing between the lenses is 300 μm, and they are fabricated in fused silica. The measured diffraction efficiency for an elliptical Gaussian beam is 80% for lenses designed using vector diffraction theory and 63% for lenses designed using scalar diffraction theory.

Ion beam figuring provides a highly deterministic method for the final precision figuring of optical components with advantages over conventional methods. The process involves bombarding a component with a stable beam of accelerated particles that selectively removes material from the surface. Figure corrections are achieved by rastering the fixed-current beam across the workpiece at appropriate, time-varying yelocities. Unlike conventional methods, ion figuring is a noncontact technique and thus avoids such problems as edge rolloff effects, tool wear, and force loading of the workpiece. This work is directed toward the development of the precision ion machining system at NASA's Marshall Space Flight Center. This system is designed for processing small (≈ 10-cm diam) optical components. Initial experiments were successful in figuring 8-cm-diam fused silica and chemical-vapor-deposited SiC samples. The experiments, procedures, and results of figuring the sample workpieces to shallow spherical, parabolic (concave and convex), and non-axially-symmetric shapes are discussed. Several difficulties and limitations encountered with the current system are discussed. The use of a 1-cm aperture for making finer corrections on optical components is also reported.

A new approach to automatic 3-D shape measurement is presented and verified by experiments. This approach, based on neural network theory, can automatically and accurately obtain the profile of diffuse 3-D objects by using a projected laser stripe. When the laser stripe is projected on an object, the line image of the laser light is grasped by a CCD camera. Using neural network theory, a relationship between the laser stripe image in the CCD camera and the related absolute position in space can be established. Thus the spatial coordinates of a measured line image in a CCD camera can be obtained according to the output value of the neural network. By processing a series of laser line images from the discrete angular positions of an object, a complete 3-D profile can be reconstructed. Theoretical analysis and experimental systems are presented. Experimental results show that this approach can determine the 360-deg profile of an object with an accuracy of 0.4 mm.

A number of fiber optic magnetostrictive transducers were fabricated using various metallic glass ribbons made of Co₇₀Fe₁₀B₂₀, Co₇₆Fe₄B₂₀, Co₈₀B₂₀, Ni, Fe₇₉B₁₆Si₅, and Fe₄₀Ni₃₈Mo₄B₁₈ and were characterized by a typical optical fiber Mach-Zehnder interferometer constructed by splicing the fiber transducers to the single-mode-fiber sensing arm. The ac magnetostrictive responses for the metallic glasses measured with the fiber optic sensing system show that the dc-bias field (H_p) for the maximum response with a Co₇₀Fe₁₀B₂₀ ribbon is ~ 0.97 Oe, that with a Ni ribbon is 23 Oe, and with a Fe₇₉B₁₆Si₅ ribbon is 5.7 Oe. A magnetostriction function describing the magnetostrictive response of the transducer was also empirically found. The measured effective magnetostrictive parameters and saturation magnetostrictions are 1.3 x 10^-7/Oe² to 7 x 10^-7/Oe² and -4.6 x 10^-6 to 5.7 x 10^-6, respectively. The optical fiber sensors exhibit minimum detectable fields H_min of the order of between 10^-5 Oe(rms)/√Hz and 10^-7 Oe(rms)/√Hz above 1 kHz at their respective dc-bias fields H_p. The H_min can be much further improved by reducing the level of noises that limit the phase resolution to ~ 10^-4 rad/√Hz in the interferometer.

Using the weakly guiding and exact field solutions of an optical fiber, we wrote a FORTRAN program to determine the fractional power that reaches the end of an optical fiber with an absorptive cladding. We have assumed that each mode of the fiber is equally excited. This corresponds to incoherent source excitation. The results were compared to a previous approximation published by Payne and Hale in 1993. We have found that, at low V-numbers, V<20, Payne and Hale's approximation deviate by more than 20% from the weakly guiding solution. At high V-numbers, the approximation deviates by less than 10%. When compared to Payne and Hale's approximation, both the weakly guiding and exact solutions are closer to the data points obtained experimentally by Degrandpre and Burgess in 1988. Although closer than Payne and Hale's approximation, our solution still deviates from the Degrandpre and Burgess results. The difference may result from the assumption that all modes were excited equally. Another possibility was the fact that we have neglected leaky modes in our treatment.

A new type of intensity-modulated sensors based on a coated light guide is presented. These sensors operate preferentially in the regime of total internal reflection (TIR), rather than relying on violation of TIR as in conventional intensity-modulated sensors. Using a physical model of the new sensor structure, the output light intensity is computed as a function of the complex reflection and transmission coefficients at the substrate-film and film-ambient interfaces. Based on the theoretical results, an experimental setup has been constructed and evaluated for measurements on various liquids. The results confirm the predicted dependence of the output signal on the characteristics of the substrate-film-ambient system. Of particular importance is the novel feature that the output signal increases as the refractive index of the ambient medium increases, at certain incidence angles.

The statistical characteristics of the amplitude and phase of an optical wave propagated through a transparent randomly varying medium are examined analytically. An optical-digital method is proposed for the detection of amplitude and phase of the randomly distorted wave. With a reference point source input, this method reveals that only a single output of the detected signal is needed to obtain both the phase and amplitude variations. The relationship between the randomly varying phase of the optical field and the detected amplitude and demodulated phase is also investigated.

This PDF file contains the editorial “Book Rvw: Ultrafast Fiber Switching Devices and Systems," by M. N. Islam for OE Vol. 34 Issue 12

This PDF file contains the editorial “Book Rvw: Lasers: Theory and Practice," by J. Hawkes and I Latimer for OE Vol. 34 Issue 12